1. Field of the Invention
The present invention relates in general to preparation of a high molecular weight polyester. More particularly, it relates to a composition and a process for preparing a high molecular weight polyester.
2. Description of the Related Arts
High molecular weight polyesters (polyesters having high intrinsic viscosity) are required for a variety of industrial uses. Such polyesters are commonly produced from low molecular weight polyesters of the same composition, in the form of particles or pellets, by solid state polymerization. However, the manufacture is time- and energy-consuming and necessitates a marked increase in manufacturing costs.
In the solid state polymerization of a polyester prepolymer, the polymerization is carried out at an elevated temperature which is below the melting point of the polyester resin. Such polymerization is normally conducted in the presence of a stream of inert gas or under a vacuum to remove volatile reaction byproducts such as ethylene glycol. This removal of the byproduct promotes the polycondensation polymerization through both the esterification and transesterification reaction mechanisms.
There have been attempts to accelerate the solid state polymerization by reducing the size of the pellets of polyester prepolymers to favor the removal of the byproduct. However, only a trivial improvement is achieved, not to mention the requirement of additional pulverizer equipment.
As further background for increasing the reaction rate of solid state polymerization, attention is directed to U.S. Pat. Nos. 4,150,214 and 5,714,262; and World Patent Application No. 9622320.